[16.08] On the Relation Between Interstellar $\rm H_2O$ and $\rm H_3O^+$ Abundances

M. Opendak (U. Pennsylvania)

The interstellar chemistry of $\rm H_3O^+$ is considered. It
is shown that within the boundaries of the model of Phillips, van
Dishoeck and Keene (1992), the abundance of $\rm H_3O^+$ actually
is not sensitive to the $\rm H_2O$, which is inconsistent with
the original conclusion of this model. Several simple
relationships are derived, which express the $\rm H_3O^+$
abundance as functions of the cosmic ray flux, $\zeta$,
fractional ionization, X(e), and the abundances of other chemical
species. Obtained formulae are applied to the cloud L134N to
specify the values of $\zeta$, X(e), $\rm H_3\, ^+$ abundance and
so on. Derived lower limits of $\zeta$ and X(e) are $1.1 \times
10^{-17}$ $\rm s^{-1}$ and $2.1 \times 10^{-8}$, respectively.
$\rm H_3O^+$ fractional abundance ranges from $2.5 \times 10^{-
9}$ to $1.5 \times 10^{-8}$ in this cloud.